A safe and effective vaccine for HIV is critically needed to combat the worldwide scourge of AIDS. While the correlates of immune protection have yet to be clearly defined, either for protective or therapeutic vaccines, it is widely believed that both CD4* and CD8 cell as well as humoral immunity are all important. How sufficiently broad, potent and sustained responses can be elicited has yet to be determined, and this represents a critical gap in our understanding of how to generate an effective vaccine such that protective immunity can be achieved. Dendritic cells (DC) represent the interface between innate and adaptive immunity and are among the most potent and important components in generating immune responses. Therefore, we have focused on novel approaches to manipulating DC in order to exploit their potential role in anti-HIV immune responses. One recently developed and particularly promising approach to priming DC is using transfection of antigen encoded mRNA. Towards this end, we developed a novel, high-efficiency method of loading DC with mRNA, and utilized this approach to maximize DC immune response generation capacity. In our preliminary studies, we have shown that mRNA encoding antigen-loaded DC are able to elicit both CD4 CD8 responses. In addition, antigen-encoded mRNA can be directly injected into mice and generate both primary and secondary T and B cell immune responses. Furthermore, our pilot data suggest that in addition to providing a mode of antigen delivery, RNA has a unique intrinsic ability to activate DC. Our hypothesis is that RNA-based dendritic cell antigen delivery offers a uniquely flexible and potent approach to immunization, that the mechanism of RNA delivery can be manipulated to regulate the types of response generated (including helper, cytotoxic and humoral immunity), and that this approach can be exploited for the development of HIV vaccines. The aim of this proposal is to better understand the mechanisms by which RNA encoded antigen is processed by DC, define the factors by which specific antigen presentation pathways may be targeted by RNA-encoded antigen, and establish proof-of-concept evidence for efficacy in HIV. We anticipate that this work will enhance our understanding of DC immune function, enable us to differentially manipulate specific elements in the immune response, and, ultimately, allow us to exploit mRNA encoded antigen loaded dendritic cell-generated immune responses for potentially protective and therapeutic purposes, in addition to providing a foundation for the rational development of a novel approach to HIV vaccine development, it is our hope that these studies may also offer a new avenue for vaccine development in general.